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Saftey first

Be careful out there people, I just ran across a 3 phase rooftop unit with a single phase disconnect installed on it. Third leg was hot all the way from breaker down stairs right to 1 leg on compressor. Volts were everywhere and I was lucky I checked with meter before touching. Even more confusing was that unit used a single phase contactor which made it appear even more like a single phase that a 3 phase. Unit is wired correctly with new disconnect.

I had a new install I was working on where an electrician did that to me. I was working late on a sat. to start the equipment up. I called the electrician right there and made them fix it, I wasn't waiting until Monday. He had to drive an hour to get to me.

Be careful out there people, I just ran across a 3 phase rooftop unit with a single phase disconnect installed on it. Third leg was hot all the way from breaker down stairs right to 1 leg on compressor. Volts were everywhere and I was lucky I checked with meter before touching. Even more confusing was that unit used a single phase contactor which made it appear even more like a single phase that a 3 phase. Unit is wired correctly with new disconnect.

I always check each leg to ground,AT THE UNIT!,not only this,always Verify your meter is working at a known voltage soure.Not only will this save you the hassel of melted fillings,it just may save your life.Point being if your meter is having a bad day,odds are you will too!

NFPA 70e

Don't forget your hardhat, faceshield, gloves, and flame-retardant clothing. You need to put those on before you shut the disconnect off. Then verify that all three legs are dead. Once dead, lock out the unit before servicing. And if you must troubleshoot with live electicity present, you must have all the gear on.

See, the human mind is kind of like... a piñata. When it breaks open, there's a lot of surprises inside. Once you get the piñata perspective, you see that losing your mind can be a peak experience. ~Jane Wagner